1. Field of the Invention
The present invention relates to an ink reservoir section for reserving ink to be supplied to the recording head used in the field of ink jet recording, and a recording head structure provided with such ink reservoir section. More particularly, the recording head structure provided with an ink reservoir section preferably usable for the ink jet recording apparatus, which is mounted on the carriage of the ink jet recording apparatus together with the ink jet recording head, and which adopts the intermittent ink supply system whereby to receive ink supplies intermittently by being connected with the main ink tank as required.
2. Related Background Art
For an ink jet recording apparatus, it has been generally practiced that an ink jet recording head is mounted on the carriage, which is guided by a guide shaft, and that recording is made in a mode having the head to scan to the left and right on a recording medium.
For the ink jet recording apparatus that records by enabling the ink jet head to scan, the so-called on-carriage type has been known to record by use of the ink jet recording head provided with nozzles for discharging ink, which is formed in the cartridge form structured to be connected with the ink tank that reserves and retains ink to be supplied to the head, having the air communication section for releasing the inside thereof to the air outside, and also, being made attachable to and detachable from the carriage (the recording head and the ink tank may be structured either inseparable or separable), which is mounted on the carriage that enables the head cartridge to scan along the guide shaft for recording.
Also, there is the so-called tube supply type, in which only the ink jet recording head is mounted on a carriage, while the tank cartridge having ink retained therein is provided for the main body side, and the ink jet recording head and the tank cartridge is connected with a flexible ink supply tube for supplying ink.
However, the weight of the on-carriage type becomes heavier, because the head cartridge, which retains ink therein, is installed on the carriage, and it tends to impede the high-speed scan of the carriage. Also, if the cartridge is made smaller in order to make it lighter, the number of recordable sheets may be made smaller inevitably in some cases.
On the other hand, there are some cases where the downsizing of an apparatus may be difficult for the tube supply type because the structure becomes complicated due to the use of the ink supply tube for connecting the ink cartridge and the ink jet recording head.
Therefore, there has been proposed the intermittent ink supply method (hereinafter, may be referred to as a pit-in method for convenience' sake) in which the recording head provided with a sub-tank is installed on the carriage, and when the carriage is in the home position or in a designated position, it is connected with the main tank provided for the apparatus main body so as to supply a predetermined amount of ink to the sub-tank on the carriage as needed.
As the ink jet cartridges used for the pit-in method ink jet recording apparatus, there is the one provided with the gas-liquid separation member formed by porous material, such as PTFE (polytetra fluoroethylene), in the sub-tank, which cuts off ink and other liquid, but allows gas to permeate, as disclosed in the specification of Japanese Patent Application Laid-Open No. 2000-334982, for example. In the case of the pit-in method, the inside of the sub-tank is negatively pressurized by sucking air through the atmosphere communication port that enables the inside of the sub-tank to be communicated with the air outside, thus inducing ink into the sub-tank from the liquid supply port provided for the sub-tank. With the gas-liquid separation member positioned in a predetermined location between the sub-tank and the atmosphere communication port, there is no possibility that ink flows out from the atmosphere communication port. Also, this functions as a valve to terminate ink filling in the status where the sub-tank is fully filled with ink (hereinafter, this valve is referred to as a “full tank valve”), thus making it possible to execute ink filling easily and reliably.
In the intermittent ink supply method disclosed in the specification of Japanese Patent Application Laid-Open No. 2000-334982, the atmosphere communication port of the ink cartridge is always released to the air outside. As a result, when the ink cartridge is installed on an ink jet apparatus, ink in the tank is evaporated from the atmosphere communication port irrespective of being in use or not.
For example, the ink tank of the on-carriage type is also provided with the atmosphere communication port, and this atmosphere communication is in the status that it is always released to the air outside, thus inviting the ink evaporation. However, in order to make such ink evaporation difficult, it is structured to arrange the ink supply path that connects the inside of the ink tank and the outer opening of the atmosphere communication port thin and long to provide a large resistance to the ink dispersion, thus reducing the ink evaporation.
Here, for the intermittent ink supply method, which is in a mode to suck the inside of the sub-tank by the application of the atmosphere communication port disclosed in the specification of Japanese Patent Application Laid-Open No. 2000-334982, the resistance to suction in the atmosphere communication port is made too great when ink is supplied to the sub-tank if the structure of the atmosphere communication port, which has a large resistance to the ink dispersion as arranged for the ink tank of on-carriage type, is adopted. As a result, it becomes impossible to supply ink into the sub-tank at high speed eventually. If such is a case, the advantages that may be brought about by the adoption of the intermittent ink supply method cannot be demonstrated. In the case of the intermittent ink supply method, therefore, it is adopted to form the structure so that resistance is made smaller in the range from the inside of the sub-tank to the atmosphere communication port for the easier suction, and the high-speed ink supply operation as well.
Consequently, it becomes inevitable that the structure tends to be such as to make the ink evaporation easier from the atmosphere communication port. As the ink evaporation advances in the sub-tank, that is, as the moisture component of ink and the solvent component are evaporated, ink becomes the one having high concentration of dyestuffs, which is the composition of ink, resulting in the images having higher density than originally anticipated, and the quality thereof is degraded. Also, if the ink evaporation further advances, ink around the nozzle portion becomes overly viscous or the dyestuffs are solidified around the nozzle portion, and ink in the nozzle portion cannot be refreshed even by the execution of the suction recovery operation. Consequently, there occurs twisted discharge direction or disabled discharges. In some cases, the discharge characteristics are deteriorated eventually.
When the apparatus is not in use, the atmosphere communication port is capped and kept in the airtight condition, hence making it possible to suppress the ink evaporation in the sub-tank. It is inevitable, then, that means is lost for easing the influence that may be exerted by the expansion and contraction of the air in the sub-tank due to the environmental changes, which may cause the temperature to change. There is a fear that the problem is encountered that ink leaks from the nozzle portion or the liquid supply port or the in-take of the air occurs in the nozzle portion or the liquid supply port, among some others. Therefore, this structure is far from being adoptable.